Summary:
IS1 is the smallest insertion sequence in E. coli. It codes for three proteins, InsA, InsB and InsAB'.

InsAB' is the transposase for IS1 [Escoubas94]. Its translation depends on a -1 frameshift within the 3' end region of insA which allows translational readthrough into insB [Sekine89]. In the absence of this frameshift, the IS1 transcriptional repressor protein InsA is produced instead [Sekine89, Escoubas94, Matsutani97].